Anticorrosive plastic packaging materials

ABSTRACT

The anticorrosive plastic packaging materials for protecting iron, aluminum and alloys of these metals against corrosion comprise synergistic mixture of contact-vapour phase corrosion inhibitors containing salt or salts selected from the salts of ammonium and alkali metals or alkaline-earth metals derived from benzoic acid and for nitrous acid and 1,3-benzodiazole and for its 1-methyl derivative and 1H-benzotriazole and/or its methyl derivative and amorphous silicium oxide. 
     As the anticorrosive plastic packaging article are predominantly used films or packaging products made of film, containers, either of mono- or multi-layer construction, wherein in case of multilayer packaging articles the synergistic mixture of contact-vapour phase inhibitors is with advantage added to the layer or layers closer to the article to be protected.

This application is a 371 of PCT/CZ99/00033 filed Oct. 4, 1999.

This invention relates to anticorrosive plastic packaging materialscomprising synergistic mixture of contact-vapour phase corrosioninhibitors, which are suitable for protection of iron, aluminum andalloys of these metals against corrosion.

BACKGROUND OF THE INVENTION

Corrosion of articles made of iron, aluminum and alloys of these metals,non-ferrous metals etc. causes their functional and aestheticdevaluation. To diminsh or completely rule out these negative phenomenanumber of methods and means of protection against corrosion areemployed, out of them the use of protective packaging materialscontaining metal corrosion inhibitors, predominantly plastics films,foams, containers etc. are the most important ones.

Most of the known plastic packaging materials comprising contact and/orvapour phase corrosion inhibitors exhibit sufficient inhibitionefficiency but only for short term protection of steel surfaces (U.S.Pat. No. 3,967,926-1976, U.S. Pat. No. 4,290,912-1981). This ispredominantly determined by the fact that the basic inhibiting componentis, according to the above references, anion of nitrous acid or primaryamine which are effective only in case of ferrous metals and theinhibition component is incorporated into the packaging material on aporous carrier. Moreover the prevailing part of known plastic packagingmaterials containing contact and/or vapour phase corrosion inhibitorscomprise salts of nitrous acid (U.S. Pat. No. 5,332,523), particularlydicyclohexylamine nitrite (U.S. Pat. No. 5,422,187-1995, patent JP63,210,285-1988, etc.) or organic salts of chromic acid, particularlycyclohexylamine chromate and dicyclohexylamine chromate (U.S. Pat. No.4,275,835-1981), which can be industrially employed only to certainextent because of their missing hygienic approval. CS AO 223373 claimsanticorrosion material containing mixture of inorganic benzoates withbenzotriazole. The JP-A-59,023,884 describes a plastic anticorrosivematerial comprising a salt of benzotriazole or its derivatives andorganic amine possibly complemented by a salt of a benzoic acid, itsderivatives, or a fatty acid and an organic amine. Use of a sodiumnitrite, sodium benzoate and benzotriazole is disclosed in FR-A-1508668but for a paper impregnation.

When silica gel appears in some anticorrosion systems, it is usuallyemployed as a desiccant or as a carrier of some anticorrosion inhibitorsparticularly of anhydrous molybdates (e.g. patents U.S. Pat. No.5,332,525, U.S. Pat. No. 5,320,778, U.S. Pat. No. 5,209,869, U.S. Pat.No. 5,393,457). In U.S. Pat. No. 5,393,457 a plastic anticorrosivepackaging material comprises besides anhydrous molybdate and silica gelalso sodium nitrite and benzotriazole.

DESCRIPTION OF THE INVENTION

The effectiveness of contact-vapour phase inhibitors is determined notonly by their suitable chemical structure but also by their vapourtension at the application temperature. To act as anticorrosiveinhibitors they have to be at first evaporated and consequentlycondensed on the surface of the metal article to be protected. Theprotecting layer is very thin, even only monomolecular, thereforesufficient inhibitor vapour tension is usually in the range of 1,33×10⁻¹to 1,33×10⁻¹ Pa at room temperature.

Anticorrosion inhibitors were originally used only in connection withanticorrosive packaging materials based on paper which was simply soakedwith inhibitor solutions practically at room temperature, so theselection of suitable compounds was less limited.

This is different in case of plastic packaging materials, e.g. lowdensity polyethylene film which is processed at temperatures above 160°C. Inhibitors have to be added to the material destined for productionof anticorrosive plastic packaging material prior to its processing andtherefore they are exposed to relatively high processing temperature andconsequently partially lost either by evaporation or sublimation. Notonly the loss of inhibitor but also emissions released causedifficulties during production and moreover increase also productioncost. Quite a few inhibitors are not sufficiently compatible withparticular plastic packaging material and exude to its surface. If themigration is too fast, the loss of inhibitor from the packaging materialis also too fast and the inherent protection period shortens. Too fastinhibitors exudation also shortens storing period of finished packagingproducts or semi-finished articles destined for their production, worsensurface appearance and touch of packaging products.

We have observed that the system of the contact-vapour phase inhibitorscomprising salts of benzoic acid and/or nitrous acid, 1,3-benzodiazoleC₇H₆N₂ and/or its 1-methyl derivative, 1H-benzotriazole and/or itsmethyl derivative of the general formula

if it is combined with suitable grades of amorphous silicium oxide formsa synergistic mixture exhibiting higher anticorrosive protection,decreases formation of emissions during packaging article production,limits exudate formation on the packaging product surface and thusimproves its appearance.

The mechanism of the observed synergy, as it is evident from the patentexamples, is explained by the interaction of N-containing inhibitorswith the surface of a selected silicium oxide grade.

The nature of anticorrosive plastics packaging materials suitable forprotecting iron, aluminum and alloys of these metals against corrosionis based on the incorporation of the synergistic mixture of thecontact-vapour phase inhibitors comprising 0,01-2,0 wt. % of the salt orthe mixture of salts of benzoic acid and/or nitrous acid and 0,001-1,5wt. % of 1,3-benzodiazole C₇H₆N₂ and/or its 1-methyl derivative and0,001-1,0 wt. % of 1H-benzotriazole C₆H₅N₃ and/or its methyl derivativeof the general formula

and 0,01-4,0 wt. % of amorphous silicium oxide SiO₂.

By the salt or mixture of salts of benzoic acid and/or nitrous acid isaccording to this invention understood the salts or the mixture of saltsof alkali metals, the salts of alkaline-earth metals and/or the salts orthe mixture of ammonium salts.

By the plastic packaging product it is according to this inventionunderstood film or packaging products made out of the film (sacks, bags,etc.), then injection or blow molded packaging products such as bottles,boxes, containers etc., made out of the anticorrosive plastic packagingmaterial.

By the plastic packaging material it is according to this inventionunderstood polyethylene and copolymers of ethylene with higher alphaolefins in the density range of 860-967 kg/m³, copolymers of ethylenecomprising 0,5-40 wt. % of vinylacetate or C₁-C₄ alkylesters of acrylicor methacrylic acid, polypropylene, copolymers of propylene withethylene and/or with higher C₄-C₈ alpha olefines having comonomercontent 0,1-10 wt. %. The plastic packaging material may also becomposed of the mixture of hereinbefore stated polymers.

The salts or the mixture of salts of benzoic and/or nitrous acid whichdo not melt at the polymer processing temperature are employed as groundmaterials having maximum particle size corresponding to ⅓ of the plasticpackaging product wall thickness. The particle size lower than 10micrometers usually meets the requirements of all the above mentionedapplications.

Preferably, the anticorrosive plastic packaging materials of theinvention are in the form of films or packaging products made of film orcontainers and/or porous emittors which are placed together with thearticle to be protected into another packaging product.

By the synergistic component of the system related to the presentinvention is constituted by the amorphous silicium oxide having meanparticle size 1-20 micrometers the actual particle size is selected withrespect to the packaging product wall thickness, and having pore volumein the range of 0,4-2,5 ml/g and pH value of 5% water suspension between4,0 and 8,0.

For the given system the SiO₂ grades having pore volumes between 1,2 and1,8 ml/g and pH values of 5% water solution in the range of 5,0-8,0 (DINISO 787-9) are the most suitable.

All components are added to the material selected for the production ofthe plastic packaging product as dry homogenised mixtures or drymixtures comprising polymer fluff However the most suitable applicationform is pelletised masterbatch of all components in the same type ofpolymer as it is used for plastic packaging product or in the polymercompatible with it.

Another possibility is to add mixture of pelletised masterbatch of allorganic components and pelletised SiO₂ masterbatch in polymerscompatible with the plastic packaging material.

All above described procedures, providing that good homogeneity of allcomponents in the packaging material is secured, guarantee that thepackaging article will exhibit the same properties.

In case that multilayer packaging product is produced it is advantageousto add all components into the inner or middle layer by the proceduresdescribed earlier.

The basic advantages of the present synergistic system when comparedwith the use of the masterbatch of mixed metal anticorrosion inhibitorsaccording to Czech application PV 1462-97v are the following: increasedanticorrosive efficiency, decreased emissions during production,particularly of large surface area articles such as films, decreasedexudation of additives to the article surface and consequently improvedsurface appearance and prolonged storage period of semi-final or finalarticles.

EXAMPLES OF INVENTION EXECUTION

The following examples illustrate the nature of the present invention:

Example 1

From the mixture comprising 10 wt. % of sodium benzoate having particlesize lower than 10 micrometers, 4,8 wt. % of 1-methyl-1,3-benzodiazole,1,2 wt. % of 1H-benzotriazole and 84 wt. % of low density polyethylenehaving melt flow index 19,6 g/10 min at 190° C. and the load of 21,2 N(CSN 640861) was with the use of a twin-screw extruder W&P ZSK 40,pelletised masterbatch A1.

From the mixture containing 8,00 wt. % of sodium benzoate havingparticle size lower than 10 micrometers, 3,84 wt. % of1-methyl-1,3-berizodiazole, 0,96 wt. % of 1H-benzotriazole, 15,00 wt. %of amorphous silicium oxide having pore volume 1,2 ml/g and meanparticle size 4 micrometers, pH value of 5% water suspension 4,5 and72,20 wt. % of the same low density polyethylene as in case of the A1masterbatch preparation, was in the same way prepared pelletisedmasterbatch denoted as B1.

Each of the two masterbatches was in the let down ratio of 4 wt. % mixedwith low density polyethylene having melt flow index 0,8 g/10 min andfrom both mixtures at the melt temperature 165° C. were prepared 100micrometers thick tubular blown films, which were in accord with thecorresponding masterbatches denoted as AIF and BIF. Both films wereanalysed to determine the content of individual inhibitors. The tablebelow shows the loss of individual components expressed in wt. % of theoriginal concentration prior to processing:

A 1 F B 1 F Sodium benzoate 3.0 2.0 1-Methyl-1,3-benzodiazole 45.0 15.01H-Benzotriazole 57.0 23.0

Steel test specimens according to {haeck over (C)}SN 411321 and aluminumones according to {haeck over (C)}SN 424105, all with polished surface,were wrapped into prepared films AIF, BIF and into the film without anyanticorrosive inhibitors (film CIF) prepared from the same basic polymerprocessed by the previously described procedure. All three films had thesame thickness 100 micrometers. After all film joints were madewatertight, the wrapped test specimens were tested according to DIN50017, KFW method (1 cycle-8 hours at 40° C. and 100% relative humidity;16 hours at 23° C. and <75% relative humidity). The following tablesummarises the test results—the number of cycles before first signs ofcorrosion appeared—rust in case of steel and surface darkening ofaluminum.

Film A 1 F Film B 1 F Film C 1 F Number of cycles Number of CyclesNumber of cycles Fe 163 >210 13 Al 135 150 10

Example 2

From the mixture containing 5,0 wt. % of sodium benzoate, 5,0 wt. % ofsodium nitrite, both having particle size lower than 10 micrometers, 6,3wt. % of 1,3-benzodiazole and 1,5 wt. % of 5-methyl-1H-benzotriazole and82,2 wt. % of the same low density polyethylene as in Example 1 wasprepared, according to procedure described also in Example 1, pelletisedmasterbatch A2.

From the mixture containing 4,0 wt. % of sodium benzoate, 4,0 wt. % ofsodium nitrite, 5,0 wt. % of 1,3-benzodiazole, and 1,2 wt. % of5-methyl-1H-benzotriazole and 18 wt. % of amorphous silicium oxidehaving pore volume 1,6 ml/g, mean particle sine 2 micrometers and pHvalue of 5% water suspension 6,0 and 67,8 wt. % of the same low densitypolyethylene as in Example 1 was prepared, according to proceduredescribed in Example 1, pelletised masterbatch B2.

Each of both masterbatches was in the amount of 6,0 wt. % homogeneouslymixed with linear polyethylene having melt flow index 1,0 g/10 min anddensity 920 kg/m³. Each of these mixtures was used for the production ofthe inner layer forming ⅔ of the twin layer film. Outer layer was formedby linear polyethylene having melt flow index 1,2 g/10 min and density932 kg/m³. Total thickness of each of both films was 62 micrometers.Tubular film extrusion technology using Alpine production line equippedwith two extruders having 35 and 50 m in diameter, respectively, at themelt temperature range of 155-175° C., was employed. The film withoutaddition of silicium oxide denoted as A2F has shown after 7 days ofstorage at room temperature slight exudation of inhibitors on thesurface while the film containing silicium oxide and marked as B2F hasnot shown, even after 2 months of storage under the same conditions, anysigns of surface changes.

Anticorrosive protection of films A2F, B2F and the film without anyanticorrosive inhibitors (C2F film) was determined according to DIN50017, KFW method, as it is described in Example 1. All films had thesame thickness.

In case of the A2F film the steel test specimens nave shown signs ofcorrosion after 48 cycles and aluminum surface darkening after 42cycles.

The testing of the B2F film was interrupted after 58 cycles without anycorrosion marks on steel and aluminum test specimens while the firstcorrosion marks of test specimens protected by the C2F film appeared onsteel after 8 cycles and on aluminum after 7 cycles.

Example 3

From the mixture comprising 8,0 wt. % of sodium benzoate, 3,8 wt. % of1,3-benzodiazole and 1.6 wt. % of 1H-bezotriazole and 86,6 wt. % of thesame low density polyethylene as in Example 1 was prepared pelletisedmasterbatch by the procedure described also in Example 1 which wasmarked A3. The masterbatch of amorphous silicium oxide in the same lowdensity polyethylene was prepared on the equipment and by the proceduredescribed in Example 1. Amorphous silicium oxide having mean particlesize 2,5 micrometers, pore volume 1,25 ml/g and pH value of 5% watersuspension 7.0 was used for the masterbatch production, the siliciumoxide concentration was 20 wt. %.

To the mixture comprising 75 wt. % of low density polyethylene havingmelt flow index 2,0 g/10 min and 25 wt. % of EVA copolymer containing 18wt. % of vinylacetate and having melt flow index 1,7 g/10 min was in onecase added 6 wt. % of the masterbatch A3 and in the other case 4 wt. %of the masterbatch A3 and 4 wt. % of the above described silicium oxidemasterbatch.

Films 100 micrometers thick were in all cases prepared by the proceduredescribed in Example 1 and were marked as A3F, B3F and the noninhibitedone as C3F. Corrosive protection was again tested according to DIN50017, KFW method described also in Example 1.

In case when the A3F film was used for protecting test specimens thecorrosion stains appeared on steel after 142 cycles and on aluminumafter 122 cycles. The test of the B3F film was interrupted after 210cycles without any visible signs of corrosion either on steel oraluminum test specimens. Corrosive damage of steel and aluminumprotected by the C3F film was observed after 12 and 9 cycles,respectively.

Industrial Utilization

Anticorrosive plastics packaging materials comprising synergisticmixtures of contact-vapour phase inhibitors of corrosion can be used forprotection against corrosion of all articles made of steel and aluminum,particularly for temporary protection of machinery articles duringtransportation and storage. The anticorrosive plastics packagingmaterials described here are applied in the form of all kinds ofpackaging films, packaging products made from films such as sacks, bagsetc. or in the form of suitable containers.

What is claimed is:
 1. Anticorrosive plastic packaging materials forprotecting an article containing iron, aluminum and alloys of thesemetals, comprising synergistic mixture of contact-vapour phaseinhibitors composed of 0.01-2.00 wt. % of salt or salts selected fromsalts of ammonium, alkali metals and alkaline earth-metals derived frombenzoic acid and/or nitrous acid and 0.001-1.5 wt. % of 1,3-benzodiazoleC₇H₆N₂ and/or its 1-methyl derivative and 0.001-1 wt. % of1H-benzotriazole and/or its methyl derivative of the general formula

0.01-4 wt. % of amorphous silicium oxide having mean particle size of1-20 micrometers, pore volume 0.4-2.5 ml/g and pH value in a 5% watersuspension in the range of 4.0-8.0 and the rest is formed by plasticmaterial.
 2. The anticorrosive plastic packaging materials as claimed inclaim 1 in which as a plastic material is used polyethylene andcopolymers of ethylene with higher alpha olefins C₄-C₈ in the 860-967kg/m³ density range, copolymers of ethylene with vinylacetate or withC₁-C₄ alkylesters of acrylic or methacrylic acid where the content ofcomonomer is in the range of 0.5-40 wt. %, polypropylene, copolymers ofpropylene with ethylene and/or with higher C₄-C₈ alpha olefins whereinthe comonomer content is 0.1-10 wt. %, or their mixtures.
 3. Theanticorrosive plastic packaging material as claimed in claim 1 being ofmono or multilayer construction wherein the synergistic mixture ofcontact-vapour phase inhibitors is added either to the layer or layerscloser to the article.
 4. The anticorrosive plastic packaging materialsas claimed in claim 1 being in the form of films or packaging productsmade of film or container and/or porous emittors which are placedtogether with the article into another packaging product.